There are already known various constructions of gas lasers, among them so-called industrial CO.sub.2 lasers which use a pure direct current transverse discharge maintained in a flowing gas stream of nitrogen, helium, and carbon dioxide at a subatmospheric pressure of, for instance, 0.1 atmosphere gauge.
It has been established that, in lasers of the above-mentioned type, both the laser efficiency and the discharge stability are sensitive to the concentration of water vapor in the gas mixture. This is so because, on the one hand, water vapor enhances the depopulation of the upper laser level of CO.sub.2 and, consequently, an increase in the water vapor amount in the gas mixture, that is, in the dew point of such water vapor, results in a decrease, albeit possibly quite small and yet not negligible, in the laser efficiency. On the other hand, however, experience has shown that the stability of the discharge decreases considerably with decreasing dew point.
Especially in low pressure (less than one atmosphere) laser systems with good vacuum integrity, prolonged running dries out the system, so that the laser efficiency increases as the dew point decreases, until a point is reached where the discharge stability, which deteriorates as the dew point decreases, becomes a major cause for concern. Therefore, it is customary or even mandatory when operating in the operating gas pressure range of, for example, 70 to 100 torr, which is typical for at least some constructions of industrial CO.sub.2 lasers, to keep the dew point in a predetermined range in order to maintain a stable discharge with good laser efficiency.
In current practice, the dew point is usually maintained in a specified range by initially allowing the laser to dry out and then adding a small amount of water to the gas mixture to keep the dew point, as measured by a hygrometer, above a specified value. Typically, the water addition is accomplished by means of water droplet injection using a manual technique or automatically through a fast-acting valve, or by moist gas introduction via a bubbler system. These methods work quite effectively, but they are susceptible to failures which may result in a situation where excessive water is sucked into the laser system. In addition, the water-drop injection often causes a noticeable fluctuation in discharge stability and subsequently in the laser output power just after injection occurs. Furthermore, the rate of electrode PG,4 corrosion or oxidation in industrial CO.sub.2 lasers with water vapor addition can be relatively high.
It has also been proposed to introduce the water vapor needed in the laser cavity not as such, but rather in the form of its constituent components, that is, hydrogen and oxygen, in the proper stoichiometric ratio. While this approach has alleviated or eliminated some of the problems mentioned above, it has not avoided the problem of electrode oxidation; as a matter of fact, in many instances it has even aggravated this problem.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a CO.sub.2 laser which does not possess the disadvantages of the known lasers of this kind.
Still another object of the present invention is to develop an arrangement for controlling the composition of the gas mixture flowing in the industrial laser of the type here under consideration in such a manner as to avoid the disadvantageous consequences stemming from the use of the heretofore known arrangements of this type.
It is yet another object of the present invention to devise a controlling arrangement of the above type, which renders it possible to accurately and predictably maintain the dew point of water vapor in the gaseous medium used by the aforementioned laser within a required range, without abrupt fluctuations which could adversely influence the laser performance.
A further object of the present invention is to design the controlling arrangement of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
A concomitant object of the present invention is to present a method of controlling the composition of the gas mixture flowing through the interior of an industrial laser, which method is particularly suited for use in the controlling arrangement of the above type.